1. Field of the Invention
The present invention relates to an overhead-valve type internal combustion engine and more particularly to a lubricating apparatus for lubricating a valve actuating mechanism by inducing oil mist within a crankcase from a breather passage into a valve actuating mechanism chamber together with a flow of blow-by gas carrying the oil mist in the overhead-valve type internal combustion engine.
2. Description of the Prior Art
As such a lubricating apparatus for the valve actuating mechanism, there have been known the ones disclosed in Japanese Laid Open Utility Model Application No. 1985-34512 (referred to as a first conventional embodiment hereinafter) and Japanese Utility Model Publication No. 1988-15530 (referred to as a second conventional embodiment hereinafter).
The lubricating apparatus according to the first conventional embodiment is constructed as follows.
That is, the breather passage for connecting the crankcase and the valve actuating mechanism chamber to each other comprises a passage inlet opened in the crankcase, a passage portion, an outlet chamber and a passage outlet opened in the valve actuating mechanism chamber arranged in order so as to be communicated to one another. The outlet chamber is formed in the space outside one of the opposite side portions of the valve actuating mechanism chamber, in which one side portion valve stems for an intake valve and an exhaust valve are arranged side by side, so as to extend along the direction of side-by-side arrangement of the valve stems. The passage outlet is opened so as to face both the valve stem and rocker arm for the exhaust valve.
Then, the lubricating apparatus according to the second conventional embodiment has following constructions different from the aforementioned first conventional embodiment.
That is, the outlet chamber of the breather passage is formed like a pipe so as to extend straight toward the valve actuating mechanism for the exhaust valve. The passage outlet is provided with two outlets, namely a first passage outlet and a second passage outlet. The first passage outlet is opened at the leading end of the pipe-like outlet chamber so as to face the contact portion between the valve stem and the rocker arm for the exhaust valve. The second passage outlet is opened in the longitudinal midway portion of the pipe-like outlet chamber so as to face the contact portion between the valve stem and the rocker arm for the intake valve.
But, there are following disadvantages associated with the aforementioned respective conventional embodiments.
In the lubricating apparatus for the valve actuating mechanism according to the first conventional embodiment, since the lubricating oil can not be supplied sufficiently to both the pivot portion of the rocker arm, the contact portion between the rocker arm and the push rod and the like located remote from the passage outlet and required to be lubricated in spite that the lubricating oil can be supplied sufficiently to the respective valve stems for the intake valve and the exhaust valve and the contact portions between the valve stems and the rocker arms, it is apprehended that those pivot portions and contact portions become short of the lubricating oil.
In the second conventional embodiment, since the supply quantity of the lubricating oil from the second passage outlet to the intake valve side is limited to a needed minimum quantity while the exhaust valve side is lubricated intensively by the lubricating oil delivered from the first passage outlet, advantageously the lubricating oil can be prevented from flowing along the valve stem of the intake valve and entering a combustion chamber. There are, however, such an unsolved problem that the portions located remote from both the passage outlets and required to be lubricated become short of the lubricating oil also in this second conventional embodiment similarly to the first conventional embodiment.